Adjustable feed mechanism for various media

ABSTRACT

A media feed mechanism in a printer is provided. The media feed mechanism includes a drive roller for feeding a print medium in the printer, a pinch roller coupled to the drive roller for feeding the print media between the drive roller and the pinch roller, and a spring operatively connected to the pinch roller for biasing the pinch roller against the drive roller to exert a pinch force on the drive roller. Such a pinch force ensures that the print medium remains in contact with and is properly fed by the drive roller. The media feed mechanism further includes means connected to the spring for altering at least one character of the biasing force provided by the spring so as to alter the pinch force exerted on the drive roller.

BACKGROUND

[0001] This invention relates generally to printers, and in particular to techniques for feeding a print medium in a printer.

[0002] In a printer, after a print medium is picked from an input tray, the print medium is advanced toward a print zone by a drive roller and an associated pinch roller. The pinch roller is biased against the drive roller for exerting a pressure or a pinch force on the drive roller so as to ensure that the print medium remains in contact with and is properly fed by the drive roller. Normally, the thicker the media, the higher pinch force is required. Also, the stiffer the media, the higher pinch force is required.

[0003] Conventionally, the pinch force is set and fixed based upon a certain type of media (nominal media) with a predetermined thickness and stiffness, for example the plain paper. Nevertheless, such a pinch force may not be suitable for a thicker or a stiffer print medium for which a higher pinch force is required.

[0004] If the pinch force is set and fixed based upon the thickest or the stiffest media, however, the force may be unnecessarily high for a print medium such as plain paper that can be much thinner. Such an unnecessarily high pinch force will result in unnecessary power consumption and may require a bigger motor for providing the high pinch force. These may not be desirable, either.

[0005] Therefore, there is a need for an improved media feed mechanism suitable for a wide range of media types.

SUMMARY

[0006] According to the present invention, a media feed mechanism in a printer includes a drive roller for feeding a print medium in the printer, a pinch roller coupled to the drive roller for feeding the print media between the drive roller and the pinch roller, and a spring operatively connected to the pinch roller for biasing the pinch roller against the drive roller to exert a pinch force on the drive roller. Such a pinch force ensures that the print medium remains in contact with and is properly fed by the drive roller. The media feed mechanism further includes means connected to the spring for altering at least one character of the biasing force provided by the spring so as to alter the pinch force exerted on the drive roller.

[0007] Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrates by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a side view showing the functional elements of a printing mechanism of an inkjet printer.

[0009]FIG. 2 illustrates a perspective view of an embodiment of a media feed mechanism in a printer;

[0010]FIG. 3 is a side elevation view of part of the media feed mechanism of FIG. 2 in a first status; and

[0011]FIG. 4 is a side elevation view of part of the media feed mechanism of FIG. 2 in a second status.

DETAILED DESCRIPTION

[0012]FIG. 1 illustrates the functional elements of a printing mechanism of an inkjet printer in which mechanism the present invention may be implemented. The printing mechanism includes a platen 109 and a feed mechanism 140 positioned adjacent the platen 109. The flat expanse of the platen 109 is positioned below an inkjet print cartridge 121 such that the platen 109 supports the print medium 130 throughout a print zone defined between the cartridge 121 and the platen 109. The print medium 130 is moved through the print zone in the direction indicated by the arrow A in FIG. 1. At the same time, the cartridge 121 performs a series of swath-like printing scans across the width of the print medium, in a direction perpendicular to the media motion direction.

[0013] The media feed mechanism 140 is ideally arranged so as to feed the print medium 130 onto the platen 109 such that the print medium presents a flat profile to the cartridge 121. Ink nozzles 125 contained in a printhead of the cartridge are thus positioned at a uniform distance from the print medium. This constant pen-to-print medium spacing ensures optimum print quality in the printer.

[0014] The media feed mechanism 140 mainly includes a drive roller 100 which is supported on a shaft 118, and a freely rotating pinch roller 102 which is biased against the drive roller 100. The shaft 118 is in turn supported by a chassis (not shown) of the printer and is coupled via a gear mechanism (not shown) to a drive motor (not shown). The pinch roller 102 operates to ensure that the print medium remains in contact with and is properly fed by the drive roller 100.

[0015] As shown in FIG. 2, the pinch roller 102 is mounted at an end of a pinch-roller-holder 104, and a tension spring 106 is attached to the other end of the pinch-roller-holder 104. A pin 116, located between the two ends of the pinch-roller-holder 104 and supported by the chassis (not shown) of the printer, functions as a pivot about which the pinch-roller-holder 104 is rotatable.

[0016] The tension spring 106 is always biased and applies a torque to the pinch-roller-holder 104. Driven by the torque, the pinch-roller-holder 104 tends to rotate about the pin 116 in a clockwise direction as indicated by arrow B in FIG. 2. As a result, the pinch roller 102 is biased against the drive roller 100, and a pinch force or a pressure is exerted on the drive roller 100 by the pinch roller 102. In other words, the torque exerted to the pinch roller holder 104 by the tension spring 106 is transferred to the pinch force on the drive roller 100. Such a pinch force ensures that the print medium 130 remains in contact with and is properly fed by the drive roller 100. In addition, the pinch force is determined by the torque exerted by the tension spring 106 and the distance between the pin 116 and the pinch roller 102. Since the distance remains unchanged, an increase or decrease of the torque will result in an increase or decrease of the pinch force accordingly.

[0017] The other end of the tension spring 106 is attached to and moves together with a linkage rod 108, which is substantially parallel to the shaft 118 and is movable in the printer between a first and a second positions as shown in FIGS. 3 and 4 respectively. The first and the second positions are configured such that the tension spring 106 exerts different torque values to the pinch roller holder 104 when the linkage rod 108 stays in different positions. Consequently, different pinch forces are exerted on the drive roller.

[0018] In FIG. 2, a z-shape level 110, which is mounted to allow rotation about an axle 113 as indicated by arrow R, is provided for driving the linkage rod 108 between the first and the second positions so as to alter the biasing force of the tension spring 106. One end 119 of the lever 110, which can be manually operated, protrudes outside the printer enclosure 115 (partially shown) through a slot opening 117 on the printer enclosure 115. The other end 120 of the lever 110 is connected to a first end of the linkage rod 108. Thereby, the rotary movement of the lever 110 produces corresponding rotational movements of the linkage rod 108 about an axis 111 of the axle 113. In this way, the linkage rod 108 is rotated between the first and the second positions.

[0019] The other end of the linkage rod 108 (hereinafter the second end) is supported by a bracket 112 and restricted to move along an opening 114 in the bracket 112. The bracket 112 is mounted on the chassis (not shown) of the printer and is preferably substantially perpendicular to the linkage rod.

[0020] As shown in FIGS. 2-4, the opening 114 is defined by a pair of semicircle profiles 126 and 128 and terminates at a first and a second ends, 122 and 124, corresponding to the first and second positions respectively. The two profiles 126 and 128 are parallel and concentric. In addition, the axis 111 of the axle 113 passes through the center “a” of the inner profile 126 of the opening 114 such that the linkage rod 108 moves along the inner profile 126 as it is rotated by the lever 110.

[0021] When a print medium not thicker than a nominal media such as a piece of plain paper is used, the linkage rod 108 stays in its first position shown in FIG. 3, that is, the linkage rod 108 is at the first end 122 of the opening 114. The tension spring 106 exerts a first biasing force and consequently a first torque to the pinch-roller-holder 104. Accordingly, the pinch roller 102 is biased against and applies a first pinch force to the drive roller 100. In addition, the linkage rod 108 is secured in the first position by the first end 122 of the opening that restrains the linkage rod 108 from movements due to the biasing force provided by the tension spring 106.

[0022] When a thicker or a stiffer print medium such as an envelope is used, a user can increase the pinch force by manually rotating the lever 110 so as to drive the linkage rod to the second position as shown in FIG. 4. The opening 114 is oriented such that as the linkage rod reaches the second end 124 of the opening, a portion 127 of the bracket defined by the inner profile 126 prevents the linkage rod 108 from movements due to the biasing force. The linkage rod will thus be secured in the second position. Furthermore, as the linkage rod 108 moves to its second position, the tension spring 106 is further stretched and consequently applies an increased biasing force to the pinch-roller-holder 104. The opening 114 is designed such that as the linkage rod 108 moves between its first and second positions, the change of the direction of the biasing force can be relatively negligible compare to the change of the amount of the biasing force. Therefore, as the linkage rod 108 moves to its second position, the tension spring 106 applies an increased torque to the pinch-roller-holder 104. As a result, the pinch force exerted on the drive roller 100 is increased accordingly.

[0023] If the increased pinch force is not desired, the user can simply rotate the lever 110 in an opposite direction to drive the linkage rod 108 back to its first position.

[0024] Alternatives can be made to the preceding embodiment. For example, a locking means (not shown) connected to the lever 110 can be provided. When the linkage rod 108 has reached its first or second position, the locking means locks and prevents the lever 110 and consequently the linkage rod 108 from rotation. In this way, the linkage rod 108 is restricted in its first or second position. Further, different types of levers can be used to replace the z-shape lever 110 illustrated in the exemplary embodiment.

[0025] Besides, the opening 114 can be oriented such that as the linkage rod 108 moves between the first and the second positions, the direction of the biasing force of the spring 106 is significantly changed while the amount of the biasing force relatively remains unchanged. Thereby, the user changes the torque applied to the pinch-roller-holder 104 and consequently the pinch force mainly by changing the direction of the biasing force. Also, it is understood that the user can change both characters of the biasing force for the purpose of this invention.

[0026] In addition, other electromechanical devices may be used to replace the manually operated lever 110. In that case, the linkage rod 108 will be automatically driven between its first and second positions when the user triggers a signal by, for example, pressing a button on the external chassis of the printer.

[0027] Further, it is understood that the media feed mechanism discussed in the preceding description can also be applied to laser printers or printing presses. 

What is claimed is:
 1. A media feed mechanism in a printer, comprising: a drive roller for feeding a print medium in the printer; a pinch roller coupled to the drive roller for feeding the print media between the drive roller and the pinch roller; a spring operatively connected to the pinch roller for biasing the pinch roller against the drive roller to exert a pinch force on the drive roller, said pinch force ensuring that the print medium remains in contact with and is properly fed by the drive roller; and means connected to the spring for altering the biasing force provided by the spring so as to alter the pinch force exerted on the drive roller.
 2. The media feed mechanism of claim 1, wherein said means includes a linkage rod to which an end of the spring attaches, and a driving means for driving the linkage rod between a first and a second positions in the printer so as to alter the biasing force.
 3. The media feed mechanism of claim 2, further comprising a securing means for securing the linkage rod in one of the first and the second positions.
 4. The media feed mechanism of claim 3, wherein the linkage rod is substantially parallel to a shaft about which the drive roller rotates.
 5. The media feed mechanism of claim 4, wherein the profile is designed to be in an arcuate shape.
 6. The media feed mechanism of claim 2, wherein the driving means includes a lever that is connected to the linkage rod and protrudes outside the printer for manual operation, the lever being manually operable so as to drive the linkage rod between the first and the second positions.
 7. The media feed mechanism of claim 6, wherein the lever is rotatable about an axle, wherein the linkage rod is movable along a profile in an semicircular shape, and wherein an axis of the axle passes through a center of the profile.
 8. The media feed mechanism of claim 1, further comprising a pinch-roller-holder, with the pinch roller mounted at one end and the spring attached to the other end thereof, wherein the spring applies a torque to the pinch-roller-holder so as to bias the pinch roller against the drive roller. 